Coking process



May 31, 1960 w. F. woLFF Erm.

coxmc PRocsss Filed sept. 2o, 195e CGKING PROCESS William F. Wolfi, ParkForest, and Philip Hill, Lansing, lll., assignors to Standard OilCompany, Chicago, lll., a corporation of Indiana Filed Sept. 20, 1956,Ser. No. 610,921

2 Claims. (Cl. 208-48) This invention relates to the coking ofhydrocarbon oils and in particular it concerns a coking process in whichcoke is easily removed from the coking zone.

in the coking of hydrocarbon oils such as petroleum the most diticultproblem has always been the removal ot coke produced from the cokingchamber. Basically, the process has been carried out by introducing theliquid petroleum fraction into a coking chamber and subjecting it to ahigh temperature to produce coke or distillates and coke. When theoperation was completed the chamber was opened and it was necessary todrill out the coke formed therein. Various methods were devised forremoving the solid coke, for example, coiled chains were placed withinthe coking chamber prior to the coking operation so that when thechamber was full of coke it could be dislodged by forcibly removing thechain which tore loose a substantial amount of the coke which had formedabout it. Another advance in removing coke from the coke chamber was toblast it out with high pressure hydraulic jets.

An object of this invention is to provide a process for coking petroleumwhich is characterized by its simplicity for removing coke from thecoking zone while minimizing or eliminating the costly mechanical meansof decoking usually associated therewith. Another object is to provide acoking process for reduced crude especially for metals contaminatedreduced crudes which produces a demetallated oil highly advantageous asa charging stock for catalytic cracking while minimizing the amount ofcoke formed which is characterized by easy removal of coke from thecoking zone and the recovery of coke therefrom generally of a smallparticle size. Other objects and advantages of the invention will beapparent from the detailed description thereof.

According to the invention, heated reduced crude is introduced directlyinto a tixed bed of water soluble salt particles e.g, rock salt whichare contained in a coking zone. The particles of the water soluble saltpreferably have a minimum cross sectional diameter greater than about1A: inch and may be in the form of lumps having a cross sectionaldiameter of 6 to l2 inches. The reduced crude is coked in the cokingzone under the usual conditions comprising a temperature between about700 and 1200 F. for a time suflicient to eiect partial or completeconversion of the reduced crude to coke and vaporous products. Thereduced crude is preferably continuously introduced into the coking zoneand the hydrocarbon products continuously withdrawn therefrom. Coke isformed on and among the void spaces of the salt particles. Aftercompletion of the coking operation when coke fills the void spacesbetween the salt particles, the introduction of reduced crude isdiscontinued. Thereafter water is introduced into the bed of saltparticles and coke, and after cooling of the bed, the Water dissolvesthe salt particles and the coke particles become dislodged and areeasily removed from the coking vessel. Since the distribution of saltparticles prevents the formation of large lumps of coke, the coke whichis thus 2,938,852 Patented May 3l, 1960 ice produced is generally of thesmall and usually regular size which does not require breaking up orcrushing prior to its use elsewhere.

In a preferred species of this invention the coking procedure describedabove is practiced upon a reduced crude having an undesirably highmetals content to prepare therefrom a demetallated highly satisfactorycatalytic cracking charge stock. In this modilication the cokingoperation is carried out under mild coking conditions comprising atemperature between about 750 and 950 F., a space velocity between about5 and 500 volumes of charged reduced crude per hour per volume of freespace in the coking zone, and the coking is carried out so that theamount of coke formed is not more than about twice (preferably about thesame amount) the Ramsbottom carbon content of the reduced crude charged.Both liquid and hydrocarbon vapors are removed from the coking zone. Inthe mild coking op eration the yields of coke, gas, and gasoline areminimized and this enables catalytic cracking of a maximum portion ofthe reduced crude and thus the production of maximum amounts ofcatalytic gasoline of high octane number.

The invention will be more clearly understood by referring to theattached drawing which illustrates in simplitied form the coking processof this invention. The embodiment of the invention illustrated hereindescribes a mild coking operation for producing demetallated catalyticcracking charge stocks from the reduced crude with a minimum formationof coke. However, the invention may also be satisfactorily used in themore severe conventional coking operation wherein from 5 to 25% of thereduced crude is converted to coke along with the formation ofhydrocarbon distillates.

Reduced crude, which may be a 5 to 75% reduced crude having a metalscontent varying between 5 and 500 ppm. or even higher, is passed fromsource 11 by way of line 12 into furnace 13 wherein it is heated to atemperature between about 700 and l200 F., herein about 800 F. Iheheated reduced crude is then passed by way of line 14 through valvedmanifolding lines 16, 17, 18 and 19 at space points directly into thebed of rock salt particles contained in coking drum 21. Coking drum 21is a vertical vessel having a supporting grid 22 with large openings ofthe order of 6 to l2 inches. Large particles of rock salt are packed ontop of the grid and vessel 21 is filled with rock salt particles of asmaller size e.g. 1A to l inch cross sectional diameter to a level suchthat a substantial amount of free space exists above the bed of rocksalt. While the water soluble salt particles employed in the embodimentshown herein is commercially available cheap rock salt, other watersoluble salts which remain solid at the coking temperatures used can beemployed. For example, such salts as Na2S04, Nazcog, K2SO4, Kgcog,MgSO4, Algso and the like can be used.

The mild coking of the reduced crude is carried out at a temperatureusually between about 750 and 950 F. employing a space velocity betweenabout 5 and 500 volumes of reduced crude charged per hour per volume offree space in the coking zone, higher space velocities being employedwith the higher temperatures. Pressures ranging from subatmospheric to500 p.s.i. or higher may be employed, somewhat lower temperatures beingused with the low pressures. By the term mild coking is meant coking thereduced crude to such an ement that the amount of coke formed is notmore than about twice the carbon residue of the reduced crude asmeasured by its Ramsbottom carbon content. This latter measurement is ameasure of the amount of carbonaceous residue which would be formed bydistilling a reduced crude 3 and it provides an indication of its cokeforming propensity. ASTM D S24-52T describes the procedurefordetermining the Ramsbottom coke. The amount of coke which 'is allowed tobe formed in the mild coking step is usually -not more than theRamsbottom carbon content of the reduced crude and is preferablyslightly less. Under such conditions a minimum amount of coke, gas andgasoline are formed together with maximum amounts of demetallatedcharging stock for catalytic cracking. lIn the embodiment shown herein,a 52% reduced crude is mildly coked at about 800 F. and a space velocityof about 50 Volumes of reduced crude charged/ hour/volume of free spacein the coking zone. Under such conditions approximately 2.5 weightpercent-coke, 20 s.c.f./ bbl. of gas and 2.5 weight percent of gasolineare formed. The hydrocarbon vapors released and formed during the cokingoperation are removed from coking drum 21 andV passed by way of line 23into line 24. Liquid hydrocarbons which trickle down through -the bed ofsalt particles are recoveerd from the bottom of coking drum 21 andpassed by way of line 26 into line 23. After the coking reaction hasvbeen carried out in vessel -21 until it is time to remove coketherefrom, the ow of reduced crude through the manifolding lines intocoking drum 21 is discontinued and reduced crude is then passed by wayof valved line 14 through manifolding lines 27, 28, 29 and 31 into thebed of rock salt particles contained in coking drum 32. Coking drum 32is thus being used while coke is being removed from coking drum 21.Obviously more coking drums can be employed, either in Series or inparallel. Coking drum 32 is the same as coking drum 21, having a bottomsupporting grid 33 upon which the large salt particles are packed withprogressively smaller sized rock salt particles placed thereabove.Hydrocarbon vapors are removed from coking drum 32 and passed by way ofline 34 into line 23. Liquid hydrocarbons are removed from below grid 33and passed by way of line 36 into line 24. The vaporous and liquidproducts are then passed by way of line 24 into cooler 37 wherein theirtemperature is reduced e.g. to about 400-500 F. They are then passed byway of line 38 into flash drum 39 wherein Xed gases and gasoline boilingrange hydrocarbons are flashed and removed overhead by Way of line 41and a liquid hydrocarbon phase is removed as a bottoms and passed by wayof line 42 to catalytic cracking. This bottoms stream comprises about95% of the reduced crude charged to the coking lstep andV approximately90% of the metals have been removed therefrom by the coking operation.4It is a highly satisfactory charging stock for catalytic cracking, muchsuperior to the reduced crude whose metals content would cause rapiddeactivation of the cracking catalyst with the formation of much largeramounts of coke and gas with lesser yields of gasoline. It has beenfound to our surprise that this demetallated reduced crude has notpicked up salt during the coking operation. vI-Evperiments have shownthat the demetal- -lated reduced crude contains less than 1 part permillion of sodium and that the coking operation has removedapproximately 90% of the metals originally present in the reduced crude.

In conducting the operation, reduced crude is charged to the coking drumuntil the amount of coke formed therein substantially fills the voidspace in the bed of salt particles. At this time, or even prior to thistime as desired, the flow of reduced crude is discontinued and coke isremoved from the coking drum. The particular time at which theriiow ofreduced crude is discontinued in order to remove coke may also begoverned by the rise in Vthe pressure drop through the bed of packedsalt particles. lf the pressure drop becomes inordinately great, it isVusually desirable to discontinue coking in -the bed coking drum andremove the coke vrtlllere'fron'i. Generally, reduced crudes should notbe introduced for a length of time such that large amounts o-f coke aredeposited above the top of the bed of salt particles, for it is muchmore diicult to dislodge the coke formed thereabove. After discontinuingthe ow of reduced crude, the bottom plate 43 of coking drum 21 isremoved. Water is passedfrom source 44 by way of valved line 46 and thenthrough manifolding lines 47, 48, 49 and 51 into coking drum 21. Steamwhich is formed is removed overhead by way of line 52, together withhydrocarbons stripped from the bed of rock salt and coke, and the heatand hydrocarbons from the stream recovered. After the bed of coke androck salt has cooled so that all of the water introduced is notvaporized, water dissolves rock salt as it trickles down through the bedof rock salt. The water passes through the opening in the bottom ofcoking drum 21 and carries coke particles into hopper 53. Hopper 53 hasopenings in its bottom which permit water to pass through. The saltcontaminated water may either be processed to recover the salt therefromor it can be passed to sewers by way of line 54 as is shown herein. Cokeparticles are removed from hopper S3 by way of screw conveyor 56. Thecoke is then passed to storage by way of line 57. As the water isintroduced intorcoking drum 21, it continues to dissolve rock salt andthe particles of coke tumble down through the vessel, through the holesin grid 22, and then into hopper 53 until substantially all of the cokeparticles are removed. Higher velocity jets of water may be used toassist in removing the more stubbornly held coke particles. These morestubbornly attached particles are rather readily removed, however, sincethey exist as a honey-combed mass due to the presence of the saltparticles during the coking operation.

After the coke has been removed from coking drum 21, particles of rocksalt are packed therein in the fashion previously described and thevessel is -then made ready for return on stream. The ilow of reducedcrude to coking drum 32 is discontinued at the proper time and the cokeis then removed from this latter coking drum in the manner describedabove. Bottom closure 58 of coking drum 32 is opened. Water is passedfrom source 59 by way of valved line 60, through manifolding lines 61,62, 63 and 64 into coking drum 32. Steam and residual amounts ofhydrocarbons are vaporized from the bed of salt particles and coke andare removed from coking drum 32 overhead by way of line 66. Use ismadeof the heat contained in this stream and the hydrocarbons therein arerecovered. Water together with dissolved salt and rock particles passthrough'grid 33 through the bottom of coking drum 32 into hopper 67. Thewater is removed from hopper 67 -through the openings in the bottom andpassed to the sewers by way of line 68. `Coke particles are removed fromhopper 67 by means of screw conveyor 69 and are then passed to storageby way of line 71.

Y While the invention has been described with reference to a certainspecific example, the invention is not to be considered as limitedthereto but includes within its scope such modications and variations aswould occur to one skilled in this art.

' What is claimed is:

1. A process of producing coke in a vessel in a form readily removablefrom said vessel which process comprises introducing hot reduced crudeinto said vessel, said vessel having contained therein a fixed bed ofwatersoluble salt particles having a minimum cross sectional diameter ofat least about 1A inch, said salt particles being solid at thetemperatures hereinafter set forth, holding said reduced crude atconditions of temperatures in the region of about 700 to 1200 F. for aresidence time sufficient to produce coke, said coke being deposited invoids between said salt particles, removing from said vessel at leastone of hydrocarbon vapors and liquid hydrocarbons, discontinuing theintroduction of reduced crude linto said vessel before said voidslare"'entirelyv` 5 filled with coke, thereafter introducing water intosaid vessel to dissolve said salt particles and to leave in said vessela porous honeycombed mass of coke, and removing water and lumps of cokefrom said vessel.

2. The method of claim 1, wherein the water-soluble 5 salt is rock salt.

References Cited inthe le of this patent UNITED STATES PATENTS 1,450,327smith Apr. s, 1923 1 6 Darlington Apr. 12, 1932 McAfee Oct. 9, 1934`Morrell Nov. 13, 1934 Atwell June 16, 1936 Mattox Jan. 25, 1955 Adams etal. Sept. 18, 1956 De Rosset Feb. 12, 1957

1. A PROCESS OF PRODUCING COKE IN A VESSEL IN A FORM READILY REMOVABLEFROM SAID VESSEL WHICH PROCESS COMPRISES INTRODUCING HOT REDUCED CRUDEINTO SAID VESSEL, SAID VESSEL HAVING CONTAINED THEREIN A FIXED BRED OFWATERSOLUBLE SALT PARTICLES HAVING A MINIMUM CROSS SECTIONAL DIAMETER OFAT LEAST ABOUT 1/4 INC. SAID SALT PARTICLES BEING SOLID AT THETEMPERATURE HEREINAFTER SET FORTH, HOLDING SAID REDUCED CRUDE ATCONDITIONS OF TEMPERATURES IN THE REGION OF ABOUT 700 TO 1200*F. FOR ARESIDENCE TIME SUFFICIENT TO PRODUCE COKE, SAID COKE BEING DEPOSITED INVOIDS BETWEEN SAID SALT PARTICLES, REMOVING FROM SAID VESSEL AT LEASTONE OF HYDROCARBON VAPORS AND LIQUID HYDROCARBONS, DISCONTINUING THEINTRODUCTION OF REDUCED CRUDE INTO SAID VESSEL BEFORE SAID VOIDS AREENTIRELY